The invention relates generally to the field of non-invasive imaging and, more particularly, to the field of processing and reconstruction of volumes based on non-invasively acquired images.
Non-invasive imaging techniques may be useful in a variety of contexts. For example, in package and passenger screening contexts, non-invasive imaging techniques allow a passenger or package to be evaluated for contraband or other illicit materials or items rapidly and with no or minimal contact. Likewise, in industrial settings, non-invasive imaging techniques allow manufactured parts or components to be checked for manufacturing defects or damage due to wear and tear which might otherwise be undetectable. For example, minute fissures or cracks may be detected within a component without having to destroy or deconstruct the component.
Perhaps the most prevalent or well-known application of non-invasive imaging however is in the medical context. For example, X-ray based techniques for obtaining images of bones or other internal structures of a patient are generally well known. Such techniques may have their limitations, however. For example, two-dimensional X-ray images, or radiographs, allow separate and distinct structures to be superimposed on one another, thereby allowing features of interest to be hidden behind otherwise uninteresting structures or allowing two or more otherwise uninteresting features to be mistaken for a feature of interest.
Further, there is no absolute scale for the intensity values, typically gray-scale values, within an image. As a result, a radiologist must typically rely on his or her experience and subjective judgment for interpretation of the image and to attribute image content to locally varying composition and/or thickness of the imaged object. In other words, the radiologist must use his or her subjective judgment and experiences to interpret the qualitatively different “light” and “dark” regions of an image into meaningful anatomical data. Such subjective determinations may be further complicated because the appearance of the image may depend on the X-ray technique used during image acquisition.
The advent of three-dimensional imaging techniques address some, but not all, of the issues related to two-dimensional images techniques noted above. For example, in tomosynthesis a limited number of radiographs acquired at different “view angles” along a limited angular range are used to reconstruct a three-dimensional volume. Such a reconstructed volume can address issues related to interpreting overlapping tissue and the resulting superimposition noted above. However, in tomosynthesis and other similar three-dimensional imaging techniques there is still no absolute quantitative relationship between voxel intensities and the material or tissue composition they represent. As a result, the interpretation of reconstructed volumes remains a subjective endeavor that relies largely on the experience and background of the reviewing radiologist or clinician. Furthermore, because the reconstructed volumes are largely dependent on the technique used to acquire the images used to reconstruct the volume, as well as on the reconstruction algorithm employed and other factors, it is difficult to compare volumes reconstructed from images acquired using different techniques or acquired at different times.